1. Field of the Invention
The present invention relates to a tape guide system for use in a video tape recorder or the like.
2. Description of the Prior Art
Tape guides for use in video tape recorders or the like are roughly classified into rotary tape guides and fixed tape guides.
The rotary tape guides are advantageous in that they impose less resistance to tapes guided thereby. However, the speeds of travel of the tapes guided by the rotary tape guides tend to reflect irregularities in the rotational speeds of bearings used in the rotary tape guides. Furthermore, if the direction in which a tape travels when it is guided by a rotary tape guide is not perpendicular to the axis of rotation of the rotary tape guide, then the tape is subjected to a transverse force applied by the tape guide. The latter drawback is aggravated when the tape is transversely shifted until an edge thereof is damaged by contact with a flange of the rotary tape guide, for example. Therefore, rotary tape guides are required to be machined and assembled with high accuracy, and hence cannot be manufactured easily.
The fixed tape guides allow tapes guided thereby to run stably, but present large resistance to the running tapes.
There has been a demand for a fixed tape guide which imposes smaller resistance to a running tape. One of such fixed tape guides that meet such a demand is an air tape guide for ejecting air from small holes defined in the surface of a guide body to float a tape off the guide body for thereby reducing the resistance applied to the tape. The air tape guide is still problematic since a compressor is required as an air pressure source.
To eliminate the drawbacks of the conventional tape guides, there has been proposed an ultrasonic vibration tape guide device as disclosed in Japanese patent application No. 02-103627. The ultrasonic vibration tape guide device employs an ultrasonic energy to reduce resistance to a running tape while allowing the tape to run stably as with fixed tape guides. The ultrasonic vibration tape guide device is adjustable in height. The heretofore proposed ultrasonic vibration tape guide device will be described below with reference to FIG. 1 of the accompanying drawings.
As shown in FIG. 1, the ultrasonic vibration tape guide device, generally designated by the reference numeral 1, includes a main shaft 5 mounted vertically on a base 18, and an ultrasonic vibrator 3 fixed to a guide member 2 that is supported on support teeth 7b of a cylindrical support shaft 7 of brass.
The ultrasonic vibrator 3 comprises a piezoelectric element having a number of piezoelectric ceramic plates with positive and negative electrodes interposed alternately therebetween. The positive electrodes are electrically connected to a positive electrode plate on one side, and the negative electrodes are electrically connected to a negative electrode plate on another side. An insulating member is attached to one end surface of the piezoelectric ceramic element, with the other end surface serving as a fixing surface.
A positive lead 3a is connected to the positive electrode plate of the ultrasonic vibrator 3, whereas a negative lead 3b is connected to the negative electrode plate of the ultrasonic vibrator 3.
The end surface serving as the fixing surface of the ultrasonic vibrator 3 is of a curved shape complementary to an outer circumferential surface of the guide member 2, and is bonded thereto.
Lower and upper flanges 9, 10 are disposed in abutment against lower and upper ends, respectively, of the support shaft 7, for guiding opposite edges of a tape wound around the guide member 2.
The main shaft 5 extends through the lower and upper flanges 9, 10 and the support shaft 7. A height adjustment screw 6 is fitted in an upper end of the support shaft 7, and threaded over a screw 23 on the upper end of the main shaft 5.
The upper flange 10 is fastened to an upper end surface of an attachment 8 by a screw 15. The lower flange 9 is fixed to a lower end surface of the attachment 8 by fixing pins 22, 24.
The attachment 8 has an ultrasonic vibrator storage space 8a defined therein which houses the ultrasonic vibrator 3. As shown in FIG. 2 of the accompanying drawings, the ultrasonic vibrator storage space 8a is defined as a hole in the shape of a rectangular parallelepiped between side walls 8b having respective stopper insertion holes 8c defined therein.
Disc-shaped stoppers 39 of rubber have engaging protrusions 39a fitted respectively in the stopper insertion holes 8c. The ultrasonic vibrator 3 is sandwiched between the stoppers 39 to prevent the guide member 2 from rotating with respect to the attachment 8.
The attachment 8 keeps the lower and upper flanges 9, 10 parallel to each other and spaced from each other by a distance that is about 0.1 mm larger than the length of the guide member 2.
As shown in FIG. 1, the lower flange 9 is normally urged upwardly under the bias of a coil spring 35 disposed around the main shaft 5 between the lower flange 9 and the base 18. The base 18 has a pin insertion hole 20 in which there is inserted an end of the fixing pin 22 that projects downwardly from the lower flange 9.
When the height adjustment screw 6 is turned, the guide member 2 is adjusted in height under or against the bias of the coil spring 35.
FIG. 3 of the accompanying drawings shows standing-wave vibrations of the guide member 2 caused when an AC voltage is applied to the ultrasonic vibrator 3, the standing-wave vibrations being illustrated along line X--X. Dotted lines N represent nodes on the guide member 2 where the vibrations have zero amplitude. The nodes N on the guide members 2 are axially spaced from the ends of the guide members 2 by a distance n, and the support teeth 7b are also axially spaced from the ends of the guide member 2 by the distance n, i.e., are positioned at the nodes N.
FIG. 4 of the accompanying drawings shows a video tape recorder 70 including a tape guide assembly 64 which incorporates two ultrasonic vibration tape guide devices 1 shown in FIGS. 1 and 2, with a tape cassette 41 being shown mounted so as to receive portions of the tape guide assembly 64 within a cavity 41a of the cassette.
As shown in FIG. 4, the tape guide assembly 64 has supply and takeup reels 42, 43, a plurality of tape guides 44, 45, 48, 49, 50, and a capstan 46 mounted on a base 40 which also supports recording and reproducing heads 47 for an audio signal or the like, and an erase head 51.
The cassette 41 has the cavity 41a defined in a front portion thereof, and tape guides 57, 58 disposed at opposite sides of the cavity 41a for guiding a tape 59 between reels 42, 43 in a run extending across the front side of the cavity 41a. The ultrasonic vibration tape guide devices 1, a pinch roller 65, and slider guides 60, 61 of the tape guide assembly 64 are positioned within the cavity 41a in back of the tape 59.
Stoppers 53, 54 serve to position the slider guides 60, 61 with respect to a rotary head drum 52. Connectors 55, 56 are attached respectively to the stoppers 53, 54 and have respective terminal pins 55a, 56a for supplying an AC voltage from the video tape recorder 70 to the slider guides 60, 61.
FIG. 5 of the accompanying drawings illustrates the position of the components of the tape guide assembly 64 when the tape 59 is drawn from the tape cassette 41 and wound around the rotary head drum 52 for recording signals on or reproducing signals from the tape 59.
More specifically, the slider guides 60, 61, the ultrasonic vibration tape guide devices 1, and the pinch roller 65 are moved from the positions shown in FIG. 4 to the positions shown in FIG. 5 for winding or loading the tape 59 around the rotary head drum 52.
At this time, respective positioning pins 60a, 61a of the slider guides 60, 61 are received and positioned in respective V-shaped grooves 53a, 54a of the stoppers 53, 54. When the ultrasonic vibration tape guide devices 1 move to the positions shown in FIG. 5, the pinch roller 65 moves into the position confronting the capstan 46. The tape guide assembly 64 now positions the tape for the recording of signals on or the reproducing of signals from the tape 59.
In each of the tape guide devices 1, the guide member 2 is ultrasonically vibrated by the ultrasonic vibrator 3 to reduce friction between the tape 59 and the guide member 2 which are held in contact with each other, for allowing the tape 59 to run smoothly. When a drive signal is applied to the ultrasonic vibrator 3 to vibrate the same, the temperature of the tape guide device 1 is increased thereby to vary the resonant frequency thereof (by 9 Hz for one degree, for example). Therefore, the tape guide devices may not be actuated for smooth tape transport at some temperatures.